1. Field of the Invention
This invention relates generally to a method of manufacturing an amorphous magnetic alloy, and especially to heat treatment of an amorphous magnetic alloy having high permeability, and high saturation magnetic induction.
2. Description of the Prior Art
In the art, a centrifugal quenching method, single roll quenching method, double roll quenching method and so on, are known methods to prepare amorphous magnetic alloys of an iron system, a cobalt-iron system, a cobalt-iron-nickel system, an iron-nickel system, and so on, which are known as soft magnetic materials. In these methods, a melt of raw material containing metal elements and so-called glass forming elements is quenched to form an amorphous alloy ribbon. In the method, internal stress .sigma. is induced in the amorphous ribbon during manufacturing, which results in deteriorated magnetic characteristics by coupling with a magnetostriction constant .lambda.. Since permeability .mu. satisfies a relation .mu..alpha.(1/.lambda..sigma.), larger internal stress results in a deteriorated permeability .mu. and an increased coersive force Hc, both of which are not desirable characteristics for soft magnetic material used as core elements of a magnetic circuit. Among various amorphous magnetic alloys, it is known that iron system amorphous alloys can be improved in permeability by annealing at an elevated temperature, under an application of a magnetic field or without the application of the magnetic field, to release the internal stress.
While, the permeability of a cobalt-iron system alloy can be improved by quenching the core shaped amorphous ribbon from a temperature T which is higher than the magnetic Curie temperature Tc of the alloy and lower than the crystallization temperature Tcry of the alloy (0.95.times.Tc.ltoreq.T&lt;Tcry).
Recently, it has been necessary to manufacture an amorphous magnetic alloy superior in not only permeability but also saturation magnetic induction Bs, to meet the requirement of high density magnetic recording in which a so-called metal magnetic tape having high coersive force is employed. In this case, the magnetic alloy used as the core of a magnetic transducer head must have a high saturation magnetic induction, for example more than 8000 gauss. In the amorphous magnetic alloy, it is necessary to increase the composition ratio of the transition metal elements such as, iron, cobalt, and nickel to obtain a high saturation magnetic induction. However, as there is a general tendency, the magnetic Curie temperature Tc of the alloy increases and the crystallization temperature Tcry of the alloy decreases upon increase of the transition metal elements. For example, in a Co-Fe-Si-B system amorphous magnetic alloy, when the total amount of Co and Fe is more than 78 atomic % of the alloy, the crystallization temperature Tcry becomes lower than the magnetic Curie temperature Tc. Thus, the above mentioned method of quenching the alloy from the temperature T satisfying the relation 0.95.times.Tc.ltoreq.T&lt;Tcry can not be applicable to the alloy containing more than 78 atomic % of Co and Fe to increase the saturation magnetic induction.
Especially in Co-Fe system amorphous alloys, the alloys have large induced magnetic anisotropy due to the existence of Co, even the alloys have high saturation magnetic induction, permeability of the alloy is rather low, and the alloy is not practically usable.